Capital Gains Tax Calculator (Long-Term)

Data Source and Methodology

Authoritative data are sourced from the IRS:

• IRS Topic No. 409 — Capital Gains and Losses (current). URL: irs.gov/taxtopics/tc409
• IRS Rev. Proc. 2023-34 (Nov. 2023) — 2024 inflation adjustments including long-term capital gain thresholds. URL: irs.gov/pub/irs-drop/rp-23-34.pdf
• Form 8960 Instructions — Net Investment Income Tax (3.8%) and MAGI thresholds. URL: irs.gov/forms-pubs/about-form-8960

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

$$
G=\max\!\big(0,\; (P - B - C) - L \big)
$$

$$
\begin{aligned}
x &= \text{taxable income excluding this gain} \\
T_0, T_{15} &= \text{upper bounds for 0% and 15% brackets (by filing status)} \\
g_0 &= \min\!\big(G,\; \max(0, T_0 - x)\big) \\
g_{15} &= \min\!\big(G - g_0,\; \max(0, T_{15} - \max(x, T_0))\big) \\
g_{20} &= \max\!\big(0,\; G - g_0 - g_{15}\big) \\
\text{LTCG Tax} &= 0\cdot g_0 + 0.15\cdot g_{15} + 0.20\cdot g_{20}
\end{aligned}
$$

$$
\begin{aligned}
\text{NII} &= G + \text{Other NII} \\
\text{MAGI} &\approx \text{user MAGI (or } x + G \text{ if not provided)} \\
T_{\text{NIIT}} &= \text{NIIT threshold (}200k~\text{Single/HOH},~250k~\text{MFJ/QW},~125k~\text{MFS)} \\
\text{NIIT base} &= \min\!\big(\text{NII},\; \max(0, \text{MAGI} - T_{\text{NIIT}})\big) \\
\text{NIIT} &= 0.038 \cdot \text{NIIT base}
\end{aligned}
$$

Glossary of Variables

Tax year

The calendar year of the transaction; this tool uses 2024 federal brackets.

Filing status

Your federal filing category: Single, Married Filing Jointly (MFJ), Married Filing Separately (MFS), Head of Household (HOH), or Qualifying Surviving Spouse (QW).

Taxable income (excluding this gain)

Taxable income before adding the current long-term gain; used to place your gain into the LTCG brackets.

Sale proceeds (P)

Total amount received from the sale.

Purchase price / Cost basis (B)

Adjusted cost basis of the asset.

Improvements & selling costs (C)

Capital improvements and transaction costs added to basis to reduce the gain.

Capital loss carryover (L)

Available capital losses applied to offset this gain.

Net long‑term gain (G)

Taxable long‑term gain after adjustments and loss offset.

Other net investment income

Other NII (interest, dividends, rents, passive income) for NIIT calculation.

Modified AGI (MAGI)

AGI adjusted for certain items, used to determine NIIT applicability.

LTCG tax

Tax calculated by allocating the gain across the 0%, 15%, and 20% brackets.

NIIT

3.8% surtax on the lesser of NII or MAGI excess over the NIIT threshold for your filing status.

Total federal tax on this gain

LTCG tax plus NIIT (if applicable).

Effective tax rate on gain

Total federal tax divided by the net long‑term gain.

After‑tax proceeds

Sale proceeds minus total federal tax on the gain.

How It Works: A Step‑by‑Step Example

Scenario: You are Single in 2024 with $85,000 of taxable income (excluding this sale). You sell stock for $250,000 that you bought for $150,000 and pay $5,000 in selling costs. You have $2,000 of capital loss carryover. NIIT is off.

1. Compute net long‑term gain: G = (250,000 − 150,000 − 5,000) − 2,000 = 93,000.
2. Determine stacking: x = 85,000. For Single in 2024, T0 = 47,025; T15 = 518,900. - 0% band available: max(0, 47,025 − 85,000) = 0 → g0 = 0. - 15% band capacity: 518,900 − 85,000 = 433,900 → g15 = min(93,000, 433,900) = 93,000. - g20 = 0.
3. LTCG tax = 0·g0 + 0.15·g15 + 0.20·g20 = 0 + 13,950 + 0 = $13,950.
4. Total federal tax on the gain = $13,950. Effective rate = 13,950 / 93,000 ≈ 15.0%.
5. After‑tax proceeds = 250,000 − 13,950 = $236,050.

Turning NIIT on with MAGI $250,000 (Single) and no other NII would add 3.8% × min(93,000, 250,000 − 200,000 = 50,000) = $1,900 of NIIT.

Frequently Asked Questions (FAQ)